Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3双层薄膜的微观结构

采用脉冲激光沉积法在(001)LaAlO_3衬底上制备了Sr_(0.5)Ba_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3薄膜,利用透射电子显微镜对薄膜的微观结构进行了研究。结果表明,底电极La_(0.5)Sr_(0.5)CoO_3在LaAlO_3衬底上外延生长并形成立方-立方取向关系。不同于块体结构,LSCO薄膜发生了结构转变,形成一种氧缺位有序调制结构。整个薄膜由大量取向畴组成,其中包含一些层错与反相畴界等缺陷。生长温度为500℃时,Sr_(0.5)Ba_(0.5)TiO_3薄膜为柱状多晶结构;当温度升高至820℃时,薄膜为缺陷较少的单晶结构。     

(0.84-x)Na_(0.5)Bi_(0.5)TiO_3-0.16K_(0.5)Bi_(0.5)TiO_(3-x)SrTiO_3系无铅压电陶瓷结构与电性能

采用固相法制备了Bi补偿的(0.84-x)Na0.5Bi0.5TiO3-0.16K0.5Bi0.5TiO3-x SrTiO3(简称NBTKBT-xST)无铅压电陶瓷,研究不同ST掺量对体系陶瓷的结构与电性能的影响规律。结果表明,在掺杂范围内(0≤x≤0.06),材料均能形成单一的钙钛矿固溶体结构。随着x的增加,陶瓷晶体结构逐渐由三方相向四方相过渡,且该体系的三方-四方准同型相界(MPB)位于0.03≤x≤0.04。在此组成区域内,体系陶瓷的铁电与压电性能较好,其中x=0.04时,材料的电性能较好:压电常数d33=156 pC/N,平面机电耦合系数k p=0.29,相对介电常数εr=1116,介质损耗tanδ=4.1%,剩余极化强度P r=30.5μC/cm2,矫顽场E c=23.9 kV/cm。介电温谱和变温电滞回线表明体系陶瓷在T d以上可能存在极性相与非极性相共存。     

Zr4+B位置换对(Pb0.5Ca0.5)(Fe(0.5)Nb0.5)O3

研究了Zr4+离子B位置换改性对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能.实验结果表明,(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3(PCFNZ)陶瓷样品呈现单一斜方钙钛矿相结构.随Zr(4+)离子的置换量增加,PCFNZ陶瓷体系的Qr值和晶粒尺寸逐渐减小;介电常数εr随着置换量增加...     

Structures and electrical properties of (Na0.5K0.5)NbO3–Li(Ta0.5Nb0.5)O3 lead-free piezoelectric ceramics

Solid solutions of (Na_0.5K_0.5)NbO₃ (NKN) and Li(Ta_0.5Nb_0.5)O₃ (LTN) were investigated as a potential candidate of lead-free piezoelectric ceramics. It was found that the Curie temperature of solid solutions increases slightly with increasing the LTN content and simultaneously the polymorphic phase transition temperature linearly decrease till below room temperature. An orthorhombic to tetragonal phase transformation at room temperature, or a morphotropic phase boundary, in NKN is induced by ~7 at% LTN addition, where the best dielectric, piezoelectric and electromechanical properties are achieved. The 0.94NKN–0.07LTN ceramics possess a dielectric constant of 765, a loss tangent of 0.04 at 1 kHz, a piezoelectric constant d₃₃ of 253 pC/N and an electromechanical coupling factor k_p of 48%.     

Ho_(0.5)Pr_(0.5)FeO_3的磁性与巨磁介电效应

采用固相反应法制备了Ho0.5Pr0.5FeO3多晶样品,对其磁性和磁介电特性进行了系统研究。在T=4.5 K附近存在Ho离子的反铁磁相变,在T=59~80K可观测到Fe离子的自旋重取向转变,磁滞回线表明样品呈现弱铁磁性。在T=270 K,介电常数可达~103,研究表明该介电常数与270 K附近的电阻变化相关联,该处电阻变小,介质损耗减小,导致介电值变大。尤其重要的是,该样品在室温下表现出磁场诱导的巨磁介电效应,在频率f=1 kHz、外加磁场为1.6×106 A/m下,其值可达5500%,该巨磁介电效应可能来源于磁电阻效应。     

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷研究进展

(Bi0.5Na0.5)TiO3(BNT)基无铅压电陶瓷体系是目前研究最广泛的功能陶瓷材料之一.综述了BNT基无铅压电陶瓷的研究现状,讨论了相关体系的设计方法、铁电性、压电性以及BNT体系的制备方法.分析比较了BNT系压电陶瓷与Pb(Zr,Ti)O3(PZT)压电陶瓷的性能差异以及存在的问题,对BNT基无铅压电陶瓷进行了展望.     

(Na0.5Bi0.5)TiO3-BaTiO3的合成与压电性能

合成了具有单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料,研究其陶瓷的压电性能.结果表明,柠檬酸与金属离子的摩尔比(C/Mn )和前驱体溶液的pH值是影响溶胶与凝胶形成的主要因素,凝胶在600℃下热处理1 h后可形成单一钙钛矿结构的(Nao.5Bi0.5)1-xBaxTiO3超细粉料.用柠檬酸盐法合成粉料的颗粒细小、化学成分均匀,有利于提高(Na0 5Bi0.5)1-xBaxTiO3陶瓷的压电性能.在准同质相界附近的组分存在较多的自发极化取向,因而表现出优良的压电性能.x=0.06时,柠檬酸盐法制备陶瓷样品的压电常数d33达到180 pC/N.     

(K0.5Na0.5)NbO3–Bi(Mg0.5Ti0.5)O3 solid solution: phase evolution, microstructure and electrical properties

Lead-free piezoelectric ceramics with the composition of (1 ? x)(K_0.5Na_0.5)NbO₃–xBi(Mg_0.5Ti_0.5)O₃ [(1 ? x)KNN–xBMT, 0 ≤ x ≤ 0.04] were synthesized via solid-state reaction method. X-ray diffraction patterns revealed that the orthorhombic—tetragonal phase transition was present for (1 ? x)KNN–xBMT with increasing the content of BMT. The study of dielectric properties illustrated that both peaks of orthorhombic—tetragonal (T _O–T ) and tetragonal—cubic (T _T–C ) phase transitions shifted to lower temperature. Through adding BMT, the electrical properties of KNN ceramics were obviously improved. The optimized piezoelectric and ferroelectric properties with d ₃₃  = 127 pC/N, k _p  = 36.58 %, P _r  = 22.1 μC/cm² were obtained as x = 0.01.     

锰氧化物La_(0.5)Sr_(0.5)MnO_3掺杂Y的改性研究

锰氧化物LaSrMnO系列材料是一类有用的自旋电子学材料。La0.5Sr0.5MnO3是一种铁磁金属性材料。利用了在La位掺杂Y的方法来改变La0.5Sr0.5MnO3的金属性而保持它的铁磁性。通过样品输运和磁化强度等的测量对La0.45Y0.05Sr0.5MnO3样品的物性进行了研究,获得了居里温度Tc=292K的亚铁磁半导体样品。     

乙二醇溶剂热法制备K_(0.5)Na_(0.5)NbO_3陶瓷粉体

采用乙二醇溶剂热法制备K_(0.5)Na_(0.5)NbO_3陶瓷粉体,系统研究了V(EG)/V(H_2O)、反应温度、前驱液浓度对粉体物相、形貌及颗粒尺寸的影响。结果表明,反应温度230℃,反应时间7h,V(EG)/V(H2O)≤3∶2可获得纯相的K_(0.5)Na_(0.5)NbO_3粉体;温度升高粉体的结晶性变差;当溶液浓度为6mol/L时,粉体出现球形和正方体两种形貌,反应物浓度增大粉体均出现正方体形貌且颗粒尺寸减小,当浓度为10mol/L、V(EG)/V(H2O)=1∶4时,粉体颗粒尺寸最小。     

(Na0.5Bi0.5)TiO3基无铅压电陶瓷研究进展

综述了（Na0.5Bi0.5)Tio3（简写为NBT）基无铅压电陶瓷的发展现状，特性及影响因素，用分子轨道理论解释了NBT强铁电性的成因，对研究较多的三个体系：NBT-ATiO3(A=Ca,Sr,Ba),NBT-BNbO3(B=Na,K)和NBT－Ln掺杂体系给予了概括介绍，内容包括成分配比，性能和应用，并提出了NBT基无铅压电陶瓷的设计原则。     

(Pb_(0.5)Sr_(0.5))TiO_3薄膜的表面化学态研究

用溶胶-凝胶法制备(Pb_(0.5)Sr_(0.5))TiO_3(简称PST)前驱体溶液,以三水醋酸铅、醋酸锶、钛酸丁酯为原料,乙二醇甲醚、去离子水、乙酰丙酮做溶剂,通过旋涂工艺在Pt/Ti/SiO_2/Si(100)基片上沉积PST薄膜.薄膜经320～380℃热分解,再经650℃退火30min,得到晶化好的薄膜样品,X射线衍射结果表明PST薄膜为钙钛矿立方相结构,其晶格常数为a=0.3919nm.用原子力显微镜观测其表面形貌,薄膜平均晶粒尺寸为300nm.用XPS测量了650℃退火PST薄膜样品的表面化学态,结果表明表面富铅,接近表面区域的原子比率Pb∶Sr∶Ti∶O是0.52∶0.50∶1.0∶3.02,接近(Pb_(0.5)Sr_(0.5))TiO_3的理想配比.     

Sm_(0.5)Sr_(0.5)CoO_(3-δ)钙钛矿型氧化物的制备与光学性能

以柠檬酸为络合剂,采用络合溶胶-凝胶法合成钙钛矿型氧化物Sm0.5Sr0.5CoO3-δ(SSC5),并通过TG-DSC、XRD、SEM、XPS和UVPC对其进行了表征。结果表明,在1 200℃保温6h后合成出粒径约为1μm左右的SSC5粉体。Sr2+取代Sm3+导致了体系中Co离子的价态发生Co2+→Co3+→Co4+转变,且在SSC5表面出现了大量的吸附氧。SSC5陶瓷片的吸收率(αS)和发射率(εT)分别为0.71和0.19,具有良好的光谱选择性。     

(1 − x)CaTiO3–x(Li0.5Nd0.5)TiO3 for ultra-small dielectrically loaded antennas

Microwave (MW) dielectric ceramics based on the solid solution (1 ? x)CaTiO₃–x(Li_0.5Nd_0.5)TiO₃ (0.25 ≤ x ≤ 1.0) were prepared by conventional solid-state synthesis using the mixed oxide route. Compositions closest to zero τ_f (+65 ppm/°C) were obtained at x = 0.8 where ε_r = 110 and the microwave quality factor, Qf ₀ ? 2600 GHz for samples sintered at 1300 °C. To reduce the sintering temperature and compensate for any Li₂O loss during fabrication, ≤0.5 wt% 0.5Li₂O–0.5B₂O₃ was added as a sintering aid in the form of raw oxides (LBR) and also as a pre-reacted glass (LBG). 0.5 wt% LBR was the most effective, reducing the temperature to achieve optimum density by ~50 °C with no significant deterioration of microwave properties (ε_r = 115, τ_f = +65 ppm/°C and Qf ₀ ? 2500 GHz). The high permittivity and relatively low sintering temperatures (1250 °C) are ideal for the development of low cost ultra-small dielectric loaded antenna, assuming the system can be tuned closer to zero by fractionally increasing x.     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

(Na0.5Bi0.5)TiO3基弛豫铁电体相变的研究进展

钛酸铋钠((Na0.5Bi0.5)TiO3,NBT)是一种典型的A位复合钙钛矿结构弛豫铁电体,具有复杂的相变序列,介电温度峰呈现明显的弛豫性.总结了NBT弛豫铁电体的相变及NBT基复合铁电体准同型相界的研究进展;从晶体结构出发,通过与B位复合型钙钛矿结构弛豫铁电体类比,对A位复合型NBT的弛豫机理进行了探讨,提出NBT弛豫性来源于其A位离子有序-无序引起的B位离子位移的变化.     

Investigation of single and multidomain Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) crystals with mm2 symmetry

The piezoelectric properties of Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) crystals with various engineered domain configurations were investigated. Rhombohedral and monoclinic∕orthorhombic crystals poled along their crystallographic [011] directions were found to possess macroscopic mm2 symmetry, with "2R" and "1O" domain, respectively. Crystals with the "2R" domain configuration were found to exhibit high extensional piezoelectric coefficients d(33) (～1300 pC∕N) and d(32) (～-1680 pC∕N), while crystals with the "1O" configuration possessed high shear coefficients d(15) (～3500 pC∕N) and d(24) (～2070 pC∕N), with relatively low extensional piezoelectric coefficients d(33) (～340 pC∕N) and d(32) (～-260 pC∕N). The observed results were explained by "polarization rotation" model, as related to their respective domain configurations.     

Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)混合导体导电性能的研究

用直流四电极法测量了空气和氮气气氛下Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF)的总电导率,用电子阻塞电极法测量了空气气氛下BSCF的氧离子电导率。结果表明575℃之前,BSCF呈现p型半导体的导电特征,总电导率温度升高而增大,随氧分压降低而减小;但在575～650℃总电导率显著下降,这与BSCF材料中晶格氧的逸出有关。通过电子阻塞电极法测得的BSCF氧离子电导率σi和温度T的关系符合Arrhe-nius公式,氧离子电导活化能Ea=140.7kJ/mol。通过透氧实验,由Wagner方程计算出来的氧离子电导率与电子阻塞电极法测量得到的值在700℃以下吻合;但700℃后,由于高氧端的气体与膜表面晶格氧的交换以及低氧端表面晶格氧与气相氧交换成为控速环节,使计算出来的氧离子电导率明显低于测量得到的值,并且二者差别随温度升高越来越大。     

La_(0.8)Ca_(0.2)Fe_(0.5)X_(0.5)O_3型氧化物的制备及其近红外发射率研究

利用固相反应法在1 300℃下合成La_(0.8)Ca_(0.2)Fe_(0.5)X_(0.5)O_3(X=Fe、Cu、Cr、Mn)氧化物,并对它们在近红外波段的发射率进行了研究和比较,通过XRD、XPS、FT-IR等对样品进行分析和表征。研究结果表明,合成的La_(0.8)Ca_(0.2)Fe_(0.5)X_(0.5)O_3型氧化物样品为单相正交晶系。掺杂后的试样较LaFeO_3在200~2 500nm近红外波段的发射率均提高60%以上,其中Ca-CrCa-CuCaCa-Mn不掺,可能是掺杂引入Fe~(4+)杂质能级增强了自由载流子浓度及其带隙之间的跃迁,不同元素掺杂引起Fe~(3+)Fe~(4+)的跃迁程度与氧空位的浓度存在差异,导致不同掺杂元素发射率不同。La_(0.8)Ca_(0.2)Fe_(0.5)X_(0.5)O_3型氧化物材料均具有优异的近红外辐射性能,能够在高温热工节能领域发挥作用。